1. Technical Field
The present invention relates to a vehicle seat belt webbing retractor in which seat belt webbing is wound on a spool which is biased for rotation in a belt retraction direction. The present invention particularly relates to a vehicle seat belt webbing retractor including a mechanism for controlling the retraction force on the belt webbing.
2. Description of the Prior Art
A typical vehicle seat belt system includes a length of belt webbing wound on a belt webbing spool of a seat belt webbing retractor. The belt webbing is extensible about a vehicle occupant to restrain the occupant. The belt webbing spool rotates in a belt withdrawal direction as the occupant withdraws belt webbing from the retractor. A rewind spring is connected with the belt webbing spool and biases the belt webbing spool for rotation in an opposite belt retraction direction.
The rewind spring exerts a retraction force on the belt webbing spool, and thus on the belt webbing. This retraction force is transmitted to the torso of the vehicle occupant through the shoulder belt portion of the belt webbing. The retraction force commonly increases as the rewind spring is wound tighter when belt webbing is withdrawn from the spool, and the belt webbing may exert an uncomfortably large amount of force on the torso of the vehicle occupant. In order to provide a constant retraction force on the belt webbing, it is known to provide a system of conical spools disposed in a force-transmitting relationship intermediate the rewind spring and the belt webbing spool.